<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
	</head>
	<body>
		<div id="app">1</div>
		
		<script>
			let num =1;
			setInterval(function(){
				num ++;
				document.getElementById("app").innerHTML = num;
			}, 1000);
			
		</script>
	</body>
</html>
